Yesterday, in a diary entry entitled
The External Cost of Energy, What You Pay With Your Flesh, I referenced a European Study showing that the environmental and health damage of various forms of energy used in Germany resulted in economic costs
beyond the cost of the energy itself. In
this study's results it was showed that the economic value of such damage varies in decreasing value (for electricity) as follows: coal (2.75), gas (1.12), solar (0.83) , nuclear (0.25), wind (0.16) and hydro (0.11). (The units of currency and energy here are Eurocents/kw-hr.)
Of course, many people will find it counter-intuitive that solar energy is more than three times as dangerous than nuclear energy, and almost 3/4's as dangerous as natural gas, but the challenge of addressing the on going crisis of global climate change will begin - if it is ever to begin - only with fresh and realistic thinking.
Were one to look into the details, it would probably come as no surprise that although nuclear power is safer than fossil fuels by an order of magnitude, the low external cost of nuclear energy is dominated by the so called "nuclear waste." Anyone who discusses nuclear energy will almost certainly hear at least one of the following statements or statements like them:
"If only `they' could figure out what to do with the waste..."
or
"nobody knows what to do with the waste,"
or
"nuclear waste will stay toxic for millions of years."
What is interesting about such responses is that implicit is such discussions is the assumption that someone has figured out what to do with the wastes of other forms of energy, in particular those associated with fossil fuels, coal for instance, where the most intractable and dangerous waste is the simple molecule carbon dioxide.
In fact nobody knows what to do with carbon dioxide. No significant repositories for carbon dioxide have ever been built; none are planned; indeed no one is even sure how one that will last (as it must) for eternity can be built.
Moreover many of the other toxins in coal - mercury for instance - will remain toxic not for millions of years, but will retain their toxicity for an infinite amount of time, or at least for as long as the earth's atmosphere contains oxygen.
The "solution" to the "problem" of fossil fuel wastes is to dump them routinely in our atmosphere, land and water with little or no restriction. Then too, one might argue that carbon dioxide might easily so impact the biosphere as to eliminate so many species as to be [i]effectively[/i] toxic for the rest of earth's history, by eliminating the vast majority of species, including perhaps the human species itself. Even if climate change does not eliminate or vastly suppress the biosphere, it is well known that many of the compounds associated with fossil fuel waste - particularly those which constitute air pollution - are powerful carcinogens responsible for many millions of deaths annually around the world.
For my money the problem of global climate change is probably the worst problem faced by humanity since the invention of literacy. It is entirely possible, likely even, that the scale of the problem is so large that it will dwarf all questions of economics, or war, of social conditions, of justice that we as a species have previously experienced.
Thus I think we'd better look at questions like "nuclear waste," a bit more carefully.
In fact the statement that "nobody knows what to do with nuclear waste," is a bit off the mark. In fact, we know a good deal about the behavior of nuclear materials, not only from our technological experience since the 1940's extending up to the present date, but from geological history extending back for billions of years.
When we contemplate the concept of "radioactive waste," we need to step back for a moment and recognize that the earth is radioactive and has always been so. It is unavoidable that in the remaining lifetime of the planet, which - as our sun is a main sequence star - we might take to be about another four or five billion years beyond the four and a half that have passed already, the earth will remain radioactive, although less so than it was in its early history. This is because almost everything on earth was once located in the core(s) of one or more very hot and short lived stars that exploded in supernovae. In these cores most of the elements now found on earth were synthesized - probably in a very short period - and ejected into the universe. Once they cooled, these elements coalesced into the planet we now call home. And so, when Joni Mitchell poetically sang, "We are stardust," she was in no way being fanciful; she was evoking a scientific fact.
Almost all of the elements originally formed were neutron enriched, and immediately were highly radioactive. However the formation of the earth and the subsequent evolution of life on the planet took a sufficiently long time that much - but certainly not all - of this radioactivity decayed away and only the radioactive elements with the longest half lives remained.
It is known, for instance, that in supernova, a commonly found isotope is aluminum-26, a radioactive substance with a half-life of 717,000 years. It is probable that a significant portion of the magnesium that we find our bodies was once this radioactive aluminum isotope. However with almost 300 half lives passed since the aluminum-26 was formed, it is likely that not even one atom of the vast quantities that must have formed remains.
Many radioactive isotopes formed in supernova are much longer lived that Aluminum-26 and have survived the 4.5 billion years since the formation of the earth. These radioactive isotopes include not only the two long lived isotopes of uranium, 235 and 238, as well as the long lived isotope of thorium, 232 - well known as nuclear fuels - but also an isotope of an element that is essential to and found in all forms of life, potassium. About 1 in every 8,500 atoms of potassium found in all living tissue is radioactive potassium-40. This may not sound like very much but given how much potassium is found on earth it turns out to be a significant amount of radioactivity. It can be shown, for instance, that the potassium content of the ocean, containing about 80 billion tons of this radioactive isotope, is responsible for about 550 billion curies of radioactivity. For comparison purposes, this is an amount of radioactivity that is between 2,000 and 10,000 times as large as the inventory of radioactivity released by the Chernobyl accident in the former Soviet Union. One must keep in mind, though that in this case the radioactivity is derives from the long half-life of potassium-40, about 1.3 billion years, and not from any human activity or technology. Note too, that only about 9% of the original potassium-40 present at the formation of the earth now remains; for most of the history of life on earth, potassium was far more radioactive than it is today.
Another radioactive element that is commonly found on earth is rubidium, an element that is very similar to potassium in its chemical behavior. A little over 1 in 4 atoms of rubidium - rubidium being the most common element found in human tissue for which no physiological function is known - are the radioactive isotope Rb-87.
The survival of long lived isotopes has had some interesting consequences in geohistory including some that are not widely known. For instance, because the half-life of another survivor from the supernova, uranium-235 - the isotope that is actually fissioned in nuclear reactors - is much shorter than the half-life of uranium-238, the more common isotope, also such a survivor, it actually happens that for a large portion of earth's history, all of the uranium on earth was what we today called "low enriched uranium." (Uranium 238 is also known as "depleted uranium.) The half-life of uranium-235 is 704 million years as opposed to 4.47 billion years, for uranium-238. Therefore more of the original uranium-235 has decayed, in a series of either 10 or 11 decays, to the stable non-radioactive isotope lead-207, while much of the uranium-238, which decays more slowly (in 15 radioactive decay steps) to lead-206, remains.
http://www.ead.anl.gov/...
Realizing this, within a few years of the first construction of artificial nuclear reactors, scientists recognized that naturally occurring nuclear reactors might have existed in geological time. This proved to be true. Many fossil examples of such reactors later were found, the first and most famous being the natural reactors at Oklo in Gabon in Africa. Almost two billion years ago, the reactors at Oklo operated in a cyclical fashion over a period of hundreds of thousands of years in pattern naturally regulated by the continuous flow of water, heat, and materials in uranium ores embedded in sandstone. The reactors thus had a passive safety feature found in almost all western reactors (a feature lacking in Chernobyl type reactors) known as a "negative void coefficient." When they got too hot, they shut down. When they cooled after shutting down, they restarted.
It happens that the behavior of many of the nuclides that resulted from the reactors' operations have been well characterized. Here is one paper that discusses the subject:
http://www.fas.org/...
When the neutrons in a nuclear reactor cause uranium atoms to split, they do not always split in the same way. Different isotopes of about 30 atomic elements are formed, with the most common fragments having atomic masses clustered around two ranges, 85-105 and 125-150. (An atomic mass may be thought of as, for the sake of approximation, the sum of the number of protons and neutrons in a nucleus. Strictly an atomic mass unit is defined as exactly 1/12 of an atom of the carbon-12 isotope.) Because the newly formed isotopes generally have more neutrons than a stable nucleus of their size can hold, they tend to be radioactive: They most often undergo nuclear decay by a process known as beta decay, during which the nucleus emits an electron and where a neutron is converted to a proton, making the original element transmute into a heavier element. Thus in the life time of spent nuclear fuel, the chemical properties of many different elements come into play.
In fact, many of the important "nuclear wastes" at these reactors, even though the area was for a long time in a rain forest, over billions of years migrated only a few meters. There are some important exceptions to this general statement, but, still the fact remains that from these reactors, we do know quite a bit about how well so called "nuclear waste," can be contained.
However I think the question of whether so called "nuclear waste," is in fact, waste at all, bears some discussion.
I will be discussing this subject in more detail in future diary entries.